Cobalt Ion Adsorption on Polyvinyl Acetal Brushes: Impact on Silica-Nanoparticle Loading During Metal Post-Chemical Mechanical Planarization Cleaning

Contamination of polyvinyl acetal (PVAc) brushes by dissolved metal ions, either from chemical mechanical planarization (CMP) or post-CMP cleaning, introduces significant challenges to device yield as semiconductor technology nodes continue to shrink to 10 nm and below. This study comprehensively investigates the chemical adsorption of cobalt (Co2+) ions and their impact on the attachment of colloidal silica (silica) to PVAc brushes under various pH conditions. The adsorption of Co2+ ions is significantly influenced by several factors, including concentration, solution pH, cobalt species (ions and hydroxides), particle size distribution (PSD), and surface charge. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that silica loading peaked at neutral pH (1006 ppb), while lower loadings were observed under acidic (522 ppb) and alkaline (213 ppb) conditions in the presence of Co2+ ions. Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses further demonstrate that Co2+ ions and silica adsorption mainly occurred through chemisorption. A density functional theory (DFT) approach was employed to optimize molecular structures and frontier orbitals, revealing that [Co(H2O)6]2+ exhibits higher reactivity compared to PVAc and silica molecules. Interaction energies (Eint) revealed that PVAc binding to unmodified silica involves weaker hydrogen bonding (Eint = 0.113 eV), whereas binding to Co2+ ions-modified silica involves stronger coordinate bonding (Eint = −8.097 eV). Overall, these results highlight the critical role of Co2+ ions in enhancing silica loading onto PVAc brushes in metal post-CMP cleaning processes.